1. Field of the Invention
The present invention relates to materials handling systems and more particularly to a novel microcomputer for controlling the operation of an S/R machine and accommodating interface of the microcomputer with a variety of peripheral devices.
2. The Prior Art
The need of industry for efficient and economic materials handling systems has long been recognized. Relatively recent efforts directed towards solving the problems associated with industrial materials handling have led to the development and use of computer-controlled warehousing systems. Computer-controlled warehousing has provided an economical solution to many of the problems associated with industrial materials handling.
Typically, the heart of a computer-controlled materials handling system is the digital computer used to control the overall warehouse operation. The primary functions of the computer controller are to receive instructions from external sources, convert the instructions from external sources into commands utilized by a storage-retriever (S/R) machine interfaced to the computer, and to send information pertaining to the execution of the instructions by the computer-controlled S/R machine as well as information as to the status and location of the materials handled to one or more operators via peripheral devices also interfaced to the computer controller. Examples of such peripheral devices are card readers, tape drives, CRT terminals, teletype printers and so forth.
The use of computer controllers as described above is well known in the art of automated materials handling systems. One type of computer controller utilized is a microcomputer located at the end of each storage aisle. See, for example, U.S. Pat. No. 3,880,299.
Typically, this type of microcomputer is specifically wired to control the operation of an S/R machine according to a predetermined program. Furthermore, the microcomputer is also typically wired to communicate with a predetermined number and kind of peripheral device. Once the microcomputer has been so wired, any additional interfacing to other devices or any change in the type of device interfaced to the microcomputer requires that the microcomputer be rewired.
Peripheral devices such as those listed above may communicate with a microcomputer in one of two ways: by serial transmission (where the bits of a character, byte or word are transmitted sequentially over a single wire) or by parallel transmission (where the bits of a character, byte or word are transmitted simultaneously over a plurality of separate wires).
Although interfacing to a serial mode peripheral device is more expensive than to interface to a parallel mode peripheral device, remote peripheral devices can communicate practically only over a serial channel. It has been found that where distortion from environmental noise is high, serial transmission of information is much more accurate, particularly over longer distances. The accuracy of serially transmitted information can be further improved by transmitting the bits of each character at a frequency which is best suited to the particular distance over which the information must be transmitted.
Currently, it is standard industry practice to build each serially communicating peripheral device such that it will send and receive information only at one of several standard rates. The frequency at which the bits of a character are transmitted is known as the baud rate. Present industry standard baud rates are 110, 150, 300, 1200, 1800, 2400, 4800 and 9600 bits per second.
Significantly, until this present invention, it was not possible to alter the number of peripheral devices interfaced to a microcomputer or to change from a serially communicating device to a parallel communicating device or to change to a serially communicating device with a different baud rate without rewiring the microcomputer. Thus, the provision of a novel microcomputer interface circuit permitting direct interface with a wide variety of peripheral devices, both serial and parallel and at any one of a variety of standard baud rates selected so as to minimize noise interference, would greatly enhance the flexibility of a computer-controlled materials handling system.
Historically, if the S/R machine malfunctioned in the process of carrying out its computer-controlled tasks, serious risk of machine damage or personal injury existed. For example, if the S/R machine extractor became disabled in the course of removing a load from high-rise storage, the S/R machine could be moved vertically or horizontally while the extractor was still projecting into a storage bay. Thus, significant damage to the system could result. Safety of the system could be improved by providing the microcomputer with a relative time circuit that automatically triggers shutdown of an S/R machine if the machine does not complete a designated task within a predetermined time increment.